Season salmon with salt and pepper. Transfer to a ziploc bag. Add teriyaki marinade; gently toss to coat. Refrigerate at least 1 hour, up to 4.
Make the dressing: Whisk together vinegar, chili sauce, fish sauce and ginger in a small bowl; set aside.
Bring a large pot of water to a boil. Add the noodles and cook to package directions. Drain and rinse under cool water to stop cooking. Set aside.
Remove salmon from marinade and rub with oil; reserve marinade. Heat a large nonstick skillet over medium-high until hot. Add salmon; cook, flipping once, until dark brown, about 3 minutes per side for medium-rare. Add about half of the reserved marinade during last minute of cooking, flip salmon to coat. Transfer to a plate. Let stand 5 minutes then flake into large chunks.
Bring 6 cups of water to a boil in a large pot. Stir in boullion powder and white parts of the scallion. Reduce to a simmer, and cook 3 minutes. Set aside.
To serve, divide noodles among 6 serving bowls; ladle some broth over noodles. Divide salmon and spinach among bowls. Drizzle with dressing; sprinkle with sesame seeds and greens of scallions. Serve immediately.